A typical microwave imaging system operates in the frequency range of 1 GHz to 100 GHz, corresponding to wavelengths in free-space of 30 cm to 0.33 cm. By comparison, optical or visible light imaging systems operate in the frequency range of 750 THz to 430 THz, corresponding to wavelengths of 0.4 μm to 0.7 μm. Though both are electromagnetic waves in nature, the different wavelengths produce different imaging characteristics. For example, microwave radiation is capable of penetrating objects that are opaque to visible light. As a result, microwave imaging systems are able to obtain measurements of the object beyond the external layer.
Traditional microwave imaging systems rely on measuring the microwave radiation from an object, and constructing an image of the object based on the radiation measurements. The radiation measurement is obtained using an antenna and adjacent receiver circuitry. The antenna can be a single element antenna, or one that is composed of an array of smaller sub-antenna elements. In addition, the antenna and the receiver circuitry can operate in a transmitting mode, a receiving mode or a combination of transmitting and receiving modes.
The measured microwave radiation includes either one or both of the amplitude and the phase of the wavefront scattered from the object. The amplitude and/or phase measurements are processed to construct an image of the object. For example, the sampled wavefront can be constructed using a Fourier-based computer image construction algorithm. An example of a Fourier-based computer image construction algorithm is described in Fourier Array Imaging by Mehrdad Soumekh (1994). However, the construction process is often computationally intensive. In addition, in many instances, the resulting constructed image suffers from poor resolution or processing artifacts, such as speckles. Therefore, what is needed is a microwave imaging system for constructing a high quality image with reduced computational complexity.